const myFil=(ary)=>{
    return ary.filter(item => item.a != '3')
    .map(item => item.a)
    .reduce((pre, item) => {
        return pre + '' + item
    }, '')
}
console.log(myFil([{a: '2'}, {a: '3'}, {a: '5'}, {a: '7'}])) 
